We propose to study several problems which bear on the mechanism of in vitro transformation of normal human lymphocytes into continuous lymphoblastoid cell lines. We shall examine the sequence of early events in transformation of purified resting B lymphocytes by Epstein-Barr virus. In particular we shall attempt to relate in time amplification of viral DNA to stimulation of cellular DNA synthesis, the appearance of EB nuclear antigen, and the first doublings of transformed cells. We shall study clonal transformants of different subclasses of human B lymphocytes in an effort to determine whether the size or physiologic state of the cell at the time of its encounter with EBV influences integration of the genome and the proportion of the genome which becomes stably associated with the cell. We shall attempt to determine whether DNA tumor viruses other than EBV can "immortalize" human lymphocytes. Our investigations will include SV40, BK virus, herpes simplex type 1 and cytomegalovirus. We will study presently available techniques and make efforts to develop new methods to infect human lymphocytes with biologically active DNA from the papovaviruses and the herpes viruses. We shall determine whether viral multiplication, transformation or viral DNA replication occurs following addition of infectious DNA to lymphocytes. Following preliminary efforts with these well characterized DNA's we plan attempts to transform lymphocytes with EBV DNA and, if successful, with specific EBV DNA fragments.